1. Field of the Invention
The present invention relates to a porous cylindrical-body module in which a plurality of porous cylindrical bodies are bundled together, a structure for supporting the porous cylindrical bodies each of which has a porous membrane on its outer circumferential surface, and a method for fastening a supporting member.
2. Description of the Related Art
For example, there is known a gas separator that includes a porous cylindrical body having a porous peripheral wall, which can be selectively permeated by a specific gas, in an airtight container. A hydrogen gas separator disclosed in, for example, JP-A H7-112111 and JP-A H6-191802 can be mentioned as such a gas separator. The aforementioned porous peripheral wall has, for example, multiple minute openings, i.e., multiple gas-permeable pores that can be permeated by the aforementioned specific gas. This porous cylindrical body is a hollow cylinder made of ceramic porous material such as alumina (Al2O3) or is a body having a porous membrane made of alumina or the like on the outer circumferential surface of the body. The specific gas is separated such that, for example, a raw gas containing the specific gas is supplied into the airtight container, and then the specific gas that has permeated the peripheral wall of the porous cylindrical body from its outer part to its inner part is taken out from an open end provided at its end and is recovered.
In the thus structured gas separator, generally, the porous cylindrical bodies are used in the form of a module in which the cylindrical bodies are bundled together in a state of being kept apart from each other in a radial direction, in order to obtain a great gas flow rate in as small a volume as possible.
FIG. 18 is a sectional view of the structure of a porous cylindrical-body module 200 housed in a high-pressure container 202 of a hydrogen gas separator, which is disclosed in JP-A H7-112111 mentioned above. In FIG. 18, the porous cylindrical-body module 200 has a structure in which an end of each of a plurality of porous cylindrical bodies 208 is airtightly fastened to, for example, a disk-shaped sealing body 206 that has closed-end holes 204 and in which the other end thereof is caused to pass through a through-hole 212 of a disk-shaped supporting body 210 and is fastened thereto. The sealing body 206 and the supporting body 210 are both made of dense alumina ceramics or the like, and the supporting body 210 is airtightly sandwiched between a pair of flanges 214 and 216 of the high-pressure container 202. Therefore, since a closed space, in which a gas that has flowed in from a gas inlet 220 cannot flow out except for a path that passes through the porous cylindrical body 208, is formed between a main body 218 of the high-pressure container 202 and the supporting body 210, the gas that has permeated the peripheral wall of the porous cylindrical body 208 inward is discharged from an open end 222.
Additionally, in the gas separator, for example, in order to fasten the porous cylindrical body to the inside of the airtight container, a supporting member made of a dense material is airtightly fastened to both ends of the gas-separating cylindrical body, i.e., to both ends of the porous cylindrical body, as disclosed in JP-A H7-163827, JP-A H8-299168, and JP-A H7-112111 mentioned above. Additionally, for example, when a plurality of porous cylindrical bodies are used in the form of a module in which the porous cylindrical bodies are bundled together in a state of being kept apart from each other in a radial direction, the aforementioned supporting member has a function to open one end of each cylindrical body toward the inside of a shared airtight chamber and to close the other end thereof.
Additionally, in a structure having a porous membrane on a porous cylindrical body, the porous membrane used herein is smaller in pore diameter than the porous cylindrical body, and, if the outer circumferential surface of the porous cylindrical body is exposed, a gas that is to be separated will pass through the exposed surface of the porous cylindrical body, and therefore desired separation efficiency cannot be obtained. Therefore, parts other than a part of the outer circumferential surface of the porous cylindrical body where the supporting member is airtightly fastened must be covered with the porous membrane.
In order to obtain this fastened state of the supporting member and the formed state of the porous membrane, for example, the hydrogen gas separator disclosed in JP-A H7-112111 mentioned above employs a supporting structure (or a fastening structure) shown in FIG. 19. This supporting structure is formed by fastening a porous cylindrical body 224 to a supporting member 226 by use of a sealing material such as frit glass and then forming a porous membrane 230 on the outer circumferential surface of the cylindrical body that has been exposed from a seal portion 22B. At this time, in order to prevent a gap from being generated between the seal portion 226 and the porous membrane 230 so as to expose the outer circumferential surface of the porous cylindrical body 224, the porous membrane 230 is formed to further cover the inner peripheral part of the supporting member 226 so as to be slightly overlapped with the seal portion 228 in an example shown in the figure.
Additionally, for example, a hydrogen gas separator disclosed in JP-A H8-299768 mentioned above employs a supporting structure shown in FIG. 20. This supporting structure is formed by providing a porous membrane 230 on the entire outer circumferential surface except both ends of a porous cylindrical body 224 and then fastening the porous membrane 230 to a supporting member 226 by use of a sealing material. At this time, in order to prevent a gap from being generated between a seal portion 228 and the porous membrane 230, the seal portion 228 is provided so as to be slightly overlapped with the porous membrane 230.
Additionally, although the yield of a gas in the porous cylindrical-body module can be raised by increasing the supply pressure of a raw gas that is supplied, for example, into an airtight container, the upper limit of the supply pressure is relatively low because the aforementioned porous material is low in strength. Therefore, as is disclosed in, for example, JP-A 2003-210951, JP-A 2002-346332, JP-A 2002-355523, and JP-A 2003-144861, the yield is raised by causing a sweep gas to flow from the other open end of the porous cylindrical body toward the aforementioned one open end.
Moreover, as a method for measuring the permeability (e.g., permeation flow rate) of the porous cylindrical-body module 200 shown in FIG. 18, there are two possible methods, i.e., a method for evaluating the characteristics of the porous cylindrical bodies 208 one by one prior to the assembly of the cylindrical bodies 208 into a module and a method for evaluating the whole of a porous cylindrical-body module 200 formed by assembling the cylindrical bodies together. According to the former method, an individual measuring operation can be easily performed, but a large amount of labor and much time are required to produce multiple porous cylindrical-body modules 200, and, disadvantageously, the airtightness and thermal shock resistance of a seal portion must be again ascertained after being modularized. Since it is difficult to stably produce porous cylindrical bodies having constant permeability, the characteristics of the whole of a module cannot be ensured by a representative value obtained by measuring a part of the cylindrical bodies.
In contrast, according to the latter method, even when multiple porous cylindrical-body modules 200 are produced, the number of measurement times can be set to be relatively small, and the airtightness and thermal shock resistance thereof can be simultaneously evaluated. However, a supporting portion 108 is produced to have a size and shape according to each of many variously sized and shaped high-pressure containers 202 so as to be airtightly sandwiched between flanges 214 and 216 of the high-pressure container 202. Therefore, disadvantageously, a measuring container that has a sealing structure according to each module is needed when the permeability and the like of the porous cylindrical-body module 200 are measured.
Additionally, the supporting structure of FIG. 19 disclosed in JP-AH7-112111 mentioned above is disadvantageously characterized in that the porous membrane 230 is broken at the boundary between the porous membrane 230 and the seal portion 228 resulting from a difference in the thermal expansion coefficient between the porous membrane 230 and the seal portion 228 after the membrane is formed and in that a seal defect by which the outer circumferential surface of the porous cylindrical body 224 is exposed is liable to occur. The porous membrane 230 is easily broken because the membrane has a small thickness of, for example, about 1 to 100 (μm). Additionally, the supporting structure of FIG. 20 disclosed in JP-A H8-299768 mentioned above is required to set its firing temperature to be lower than a temperature that is reached when the porous membrane 230 is formed, because the seal portion 228 is formed after the membrane is formed. Therefore, disadvantageously, bonding strength cannot be secured resulting from the lowness of the firing temperature. Although JP-A H7-163827 and JP-A H8-299768 describe an aspect in which the firing temperature that is reached when the supporting member 226 is fastened is set to be higher than the temperature reached when the porous membrane 230 is formed, this manufacturing condition allows the porous membrane 230 to deteriorate and be easily broken during manufacture or during use. Additionally, although JP-A H7-163827 describes a structure in which the porous membrane 230 is formed on the whole of the outer circumferential surface of the porous cylindrical body 224, sufficient bonding strength cannot be obtained because the porous cylindrical body 224 is joined through the porous membrane 230 in the thus formed structure. Without being limited to the use application of a gas separation, this problem will likewise arise in various use applications such as liquid filtration when the porous cylindrical body 224 having the porous membrane 230 is structured to be supported by the supporting member 226.
Additionally, as described in JP-A2003-210951 mentioned above, the conventional porous cylindrical-body module that can supply a sweep gas has a structure in which the sweep gas is sent from the side of one end of the porous cylindrical body in the airtight container, and a separated gas and the sweep gas are recovered from the side of the other end thereof. Therefore, disadvantageously, a space where the airtight container is disposed becomes large in the porous cylindrical-body module that can supply a sweep gas, because an opening used to introduce the sweep gas and an opening used to recover the other gases are provided at positions opposite to each other in the airtight container.